Reduced debris milled multilateral window

ABSTRACT

A reduced debris milled multilateral window. In a described embodiment, a window joint is constructed in a manner which reduces debris created when a window is milled therethrough. The window joint includes a generally tubular body having a sidewall, a window portion of the sidewall being configured for forming a window therethrough, and a thickness of the sidewall being reduced in the window portion.

BACKGROUND

[0001] The present invention relates generally to operations performedand equipment utilized in conjunction with subterranean wells and, in anembodiment described herein, more particularly provides a reduced debrismilled multilateral window.

[0002] In multilateral wells it is common practice to drill a branch orlateral wellbore extending laterally from an intersection with a main orparent wellbore. A casing string is typically installed in the parentwellbore, a whipstock is positioned in the casing string at the desiredintersection, and then one or more mills are deflected laterally off ofthe whipstock to form a window through the casing sidewall.

[0003] Unfortunately, this milling process usually produces a largeamount of debris, such as small pieces of the metal casing, whichaccumulate in the parent wellbore. This debris may make the whipstockdifficult to retrieve after the milling process is completed. Even afterthe whipstock is retrieved, the debris may cause other problems, such asplugging flow control devices, damaging seals, obstructing seal bores,interfering with passage of equipment past the intersection, etc.

[0004] One proposed solution is to pre-mill the window in the casing,that is, form the window through the casing sidewall prior to installingthe casing in the parent wellbore. However, if the casing is to becemented in the main wellbore, the window should be closed during thecementing operation, such as by using an internal or external sleeve.Typically, the sleeve is made of an easily milled material, such asaluminum or a composite material, or is made so that it can be retrievedafter the cementing operation.

[0005] Although such sleeves have achieved some success, they also havetheir problems. For example, the sleeve material may be incompatiblewith fluids used in the well. The use of an external sleeve increasesthe casing outer diameter, requiring either a smaller casing size to beused, or a larger wellbore to be drilled. The use of an internal sleevereduces the casing inner diameter, restricting the passage of fluids andequipment through the casing. The use of a shiftable or retrievableinner sleeve requires another operation in the well and increases thecomplexity of the equipment and the procedure.

[0006] From the foregoing, it can be seen that it would be quitedesirable to provide improved apparatus, systems and methods for formingwindows in casing.

SUMMARY

[0007] In carrying out the principles of the present invention, inaccordance with an embodiment thereof, a window joint is provided forinterconnection in a casing string. The use of the window joint reducesthe debris created when a window is milled through the window joint.

[0008] In one aspect of the invention, a window joint is provided whichincludes a generally tubular body having a sidewall. A window portion ofthe sidewall is configured for forming a window therethrough. Athickness of the sidewall is reduced in the window portion using avariety of techniques.

[0009] In another aspect of the invention, a window joint system isprovided which includes a window joint interconnected in a casing stringand positioned in a parent wellbore. The window joint includes asidewall having a window portion through which a window is formed todrill a branch wellbore. The window portion has a reduced thickness ofthe sidewall prior to forming the window through the window portion.

[0010] In yet another aspect of the invention, a method of drilling abranch wellbore extending laterally from an intersection with a parentwellbore is provided. The method includes the steps of: interconnectinga window joint in a casing string, the window joint including a sidewallhaving a window portion with a reduced thickness of the sidewall;positioning the casing string in the parent wellbore; aligning thewindow joint with the window portion facing toward the desired branchwellbore; cutting through the window portion of the window joint,thereby forming a window through the sidewall; and drilling the branchwellbore through the window.

[0011] These and other features, advantages, benefits and objects of thepresent invention will become apparent to one of ordinary skill in theart upon careful consideration of the detailed description ofrepresentative embodiments of the invention hereinbelow and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic partially cross-sectional view of a methodembodying principles of the present invention;

[0013]FIG. 2 is a schematic cross-sectional view of a first window jointembodying principles of the invention;

[0014]FIG. 3 is a cross-sectional view of the first window joint, takenalong line 3-3 of FIG. 2;

[0015]FIG. 4 is a schematic cross-sectional view of a second windowjoint embodying principles of the invention;

[0016]FIG. 5 is a cross-sectional view of the second window joint, takenalong line 5-5 of FIG. 4;

[0017]FIG. 6 is a schematic cross-sectional view of a third window jointembodying principles of the invention;

[0018]FIGS. 7A & B are alternate cross-sectional views of the thirdwindow joint, taken along line 7-7 of FIG. 6; and

[0019]FIG. 8 is an elevational side view of a fourth window jointembodying principles of the invention.

DETAILED DESCRIPTION

[0020] Representatively and schematically illustrated in FIG. 1 is amethod 10 which embodies principles of the present invention. In thefollowing description of the method 10 and other apparatus and methodsdescribed herein, directional terms, such as “above”, “below”, “upper”,“lower”, etc., are used only for convenience in referring to theaccompanying drawings. Additionally, it is to be understood that thevarious embodiments of the present invention described herein may beutilized in various orientations, such as inclined, inverted,horizontal, vertical, etc., and in various configurations, withoutdeparting from the principles of the present invention.

[0021] In the method 10, a main or parent wellbore 12 is drilled and acasing string 14 is installed and cemented in the wellbore. The terms“parent” and “main” wellbore are used herein to designate a wellborefrom which another wellbore is drilled. A parent or main wellbore doesnot necessarily extend directly to the earth's surface, but couldinstead be a branch of yet another wellbore.

[0022] The term “casing” is used herein to designate a tubular stringused to line a wellbore. Casing may actually be of the type known tothose skilled in the art as “liner”, and may be made of any material,such as steel or composite material, and may be segmented or continuous,such as coiled tubing.

[0023] The casing string 14 in the method 10 includes a window joint 16interconnected therein. An internal orienting profile 18 may be formeddirectly on the window joint, or it may be separately attached theretoas depicted in FIG. 1. The window joint 16 is positioned at a desiredintersection 22 between the parent wellbore 12 and a branch or lateralwellbore 20 to be drilled later.

[0024] The terms “branch” and “lateral” wellbore are used herein todesignate a wellbore which is drilled outwardly from its intersectionwith another wellbore, such as a parent or main wellbore. A branch orlateral wellbore may have another branch or lateral wellbore drilledoutwardly therefrom.

[0025] The window joint 16 and orienting profile 18 are rotationallyoriented relative to the branch wellbore 20 using techniques known tothose skilled in the art, such as by using a gyroscope engaged with theorienting profile.

[0026] The parent wellbore 12 below the intersection 22 may be completedbefore or after the branch wellbore 20 is drilled (or not at all). Asdepicted in FIG. 1, the lower parent wellbore 12 has been completed andhas a packer 24 installed therein. The packer 24 includes an internalseal bore or PBR 26.

[0027] When it is desired to drill the branch wellbore 20, a whipstockor deflector 28 is positioned in the casing string 14 below theintersection 22. Keys or dogs 30 carried on the whipstock cooperativelyengage the orienting profile 18. This engagement anchors the whipstock28 to the casing string 14 and rotationally orients an inclineddeflector surface 32 so that it faces toward the desired branch wellbore20.

[0028] One or more cutting tools, such as mills and drills, are thenlowered through the casing string 14 and deflected laterally off of thedeflector surface 32 to form a window 34 through the casing and to drillthe branch wellbore 20. In prior art methods, this process of formingthe window 34 has resulted in a large quantity of debris accumulating inthe parent wellbore 12 at and below the intersection 22. Although thewhipstock 28 might have been equipped with a debris barrier 36 in theseprior art methods, the debris could still hamper retrieval of thewhipstock from the well, interfere with passage of equipment through theintersection 22, cut seals (such as packing elements on the packer 24),prevent sealing in seal bores (such as the seal bore 26), or cause otherdifficulties.

[0029] The present invention, however, substantially reduces the debriscreated in milling the window 34, which reduces or eliminates theproblems described above. These advantages are achieved in the method 10without requiring the use of an internal or external sleeve.Nevertheless, a sleeve could be used in the method 10, if desired,without departing from the principles of the invention.

[0030] To achieve these benefits, the window joint 16 used in the method10 has a reduced thickness sidewall in a window portion of the windowjoint. This reduced thickness results in less debris being created whenthe window 34 is milled. Although reduced, the sidewall thickness in thewindow portion is still sufficient to prevent cement, or other fluids orgases, from flowing therethrough when the casing string 14 is installedand cemented in the parent wellbore 12.

[0031] The reduced thickness of the window portion of the window joint16 makes the sidewall lighter in the window portion, and so the oppositeside of the window joint is influenced by gravitational force to seekthe lower side of the wellbore 12 when the casing string 14 isinstalled. The parent wellbore 12 is depicted in FIG. 1 as beingsubstantially vertical, but those skilled in the art understand thatthis situation is very rare, since most wellbores are actually deviatedat least somewhat from true vertical.

[0032] Preferably, the branch wellbore 20 is drilled so that it extendsat least partially upwardly from the parent wellbore 12. Therefore it isa significant benefit for the side of the window joint 16 opposite thewindow portion to seek the lower side of the wellbore 12 when the casingstring 14 is installed.

[0033] Representatively and schematically illustrated in FIGS. 2-8 arevarious window joints which may be used for the window joint 16 in themethod 10. These various specific examples of window joints aredescribed herein to show how the principles of the invention may beincorporated into the construction of window joints, but it is to beclearly understood that the principles of the invention are not limitedto the details of these specific examples. Instead, the principles ofthe invention permit a wide variety of window joint constructions.

[0034] In addition, it should be clearly understood that the principlesof the invention may be incorporated into methods other than the method10, such as methods wherein a whipstock is not used. The window jointexamples described below, and other window joints embodying principlesof the invention, may be used in these other methods, as well.

[0035] In FIGS. 2 & 3 a window joint 40 having an internal orientingprofile 42 formed in a tubular body 38 of the window joint is depicted.Preferably, the orienting profile 42 is formed directly on the windowjoint 40, so that the separate steps of connecting the orienting profileto the window joint and rotationally aligning the profile with thewindow joint are avoided. However, the orienting profile 42 could beformed in a separate element, such as a collar, if desired.

[0036] The window joint 40 has a sidewall 46 that is a consistentthickness at upper and lower end connections 48 of the window joint. Theend connections 48 may be provided with conventional threads, seals,seal bores, or welds, etc. (not shown) for interconnection in a tubularstring. However, between the end connections 48, the window joint 40includes a window portion 44 having a reduced sidewall 46 thickness.

[0037] This reduced sidewall 46 thickness is formed by laterallyoffsetting an inner diameter 50 in the window portion 44 relative toinner diameters 52 at the end connections 48. That is, a longitudinalcenterline 54 of the window portion 44 is laterally offset relative to alongitudinal centerline 56 of the end connections 48. However, note thatthe window joint 40 has the same outer diameter 58 at the window portion44 and at the end connections 48, resulting in the inner diameter 50being also laterally offset relative to the outer diameter 58.

[0038] The offset inner diameter 50 may be formed in the window joint 40using various methods. For example, the inner diameter 50 may be cutusing a lathe, or the window joint could be cast, forged or drawn withthe offset inner diameter.

[0039] In FIGS. 4 & 5 another window joint 60 is depicted. A sidewall 62of the window joint 60 has a reduced thickness in a window portion 64.The reduced thickness is due to a recess 66 formed internally on thesidewall 62. The recess 66 may be formed by milling, casting, forging,or any other method.

[0040] One advantage of using an internally formed recess is that therecess may be used for additional purposes. For example, a whipstock ordeflector 68 may carry a member 70 which engages the recess 66 toposition and rotationally align a deflector face 72 relative to thewindow portion 64.

[0041] In FIGS. 6, 7A & B another window joint 80 is depicted. Thewindow joint 80 has a sidewall 82 with a reduced thickness in a windowportion 84 between end connections 86. The window joint 80 can alsoinclude an orienting profile, such as the profile 42 described above,and can also include one or more internal recesses, such as the recess66 described above, formed on the window portion 84.

[0042] The cross-sectional views in FIGS. 7A & B depict alternatemethods of forming the reduced sidewall thickness in the window portion84. In FIG. 7A, the reduced thickness is formed by cutting (or casting,forging, drawing, etc.) a laterally offset, but larger radius 88 on anouter radius go of the window joint 80. The radius go has a longitudinalcenterline 92, which also corresponds to inner and outer diameters 94,96 of the window joint 80. However, a centerline 98 of the radius 88 islaterally offset relative to the centerline 92.

[0043] Thus, the window portion 84 includes multiple intersectingexternal radii 88, go. One benefit of this construction is that thesidewall thickness of the window portion 84 gradually increases toeither side between the radius 88 and the inner diameter 94 in thewindow portion, providing increased support against collapse of thewindow portion.

[0044] Although the window joint 80 as depicted in FIG. 7A has theradius 88 greater than the radius go, it should be understood that theradii could be the same, or the radius 88 could be smaller than theradius go.

[0045] In FIG. 7B the window joint 80 is depicted with the reducedsidewall thickness being due to a recess 100 formed externally on thewindow portion 84. The recess 100 may be formed by milling, casting,forging, or any other method. Note that any shape of the recess 100 maybe used in keeping with the principles of the invention.

[0046] For example, instead of the recess 100 being curved about thecircumference of the sidewall 82, as depicted in FIG. 7B, the recesscould be straight, etc. Although the recess 100 is depicted in FIG. 7Bas extending only a portion of the length of the window joint 80, therecess could extend the entire length of the window joint.

[0047] In FIG. 8 another window joint 110 is depicted which is similarto the window joint 80. However, the window joint 110 includes a windowportion 116 having multiple recesses 112 formed externally thereon.Between the recesses 112, circumferentially extending ribs 114 aredisposed to support the reduced sidewall thickness resulting from therecesses.

[0048] The window joint 110 may alternatively, or in addition, have oneor more recesses formed internally thereon, such as the recess 66described above, and if multiple internal recesses are used, supportingribs may be formed between the internal recesses.

[0049] Of course, a person skilled in the art would, upon a carefulconsideration of the above description of representative embodiments ofthe invention, readily appreciate that many modifications, additions,substitutions, deletions, and other changes may be made to thesespecific embodiments, and such changes are contemplated by theprinciples of the present invention. Accordingly, the foregoing detaileddescription is to be clearly understood as being given by way ofillustration and example only, the spirit and scope of the presentinvention being limited solely by the appended claims and theirequivalents.

What is claimed is:
 1. A window joint, comprising: a generally tubularbody having a sidewall, a window portion of the sidewall beingconfigured for forming a window therethrough, and a thickness of thesidewall being reduced in the window portion.
 2. The window jointaccording to claim 1, wherein the body further has an orienting profileformed internally therein.
 3. The window joint according to claim 2,wherein the orienting profile is rotationally aligned with the windowportion of the sidewall.
 4. The window joint according to claim 1,wherein the window portion has an outer diameter laterally offsetrelative to an inner diameter of the window portion.
 5. The window jointaccording to claim 1, wherein the window portion has an inner diameterwith a longitudinal centerline laterally offset relative to alongitudinal centerline of end connections of the window joint.
 6. Thewindow joint according to claim 1, wherein the window portion has arecess formed externally on the body sidewall to reduce the thickness ofthe sidewall.
 7. The window joint according to claim 1, wherein thewindow portion has a recess formed internally on the body sidewall toreduce the thickness of the sidewall.
 8. The window joint according toclaim 1, wherein the window portion has an external radius formedthereon which reduces the thickness of the sidewall.
 9. The window jointaccording to claim 1, wherein the window portion has multiple radiiformed externally thereon.
 10. The window joint according to claim 1,wherein the window portion has multiple recesses formed in the sidewall,the sidewall between the recesses forming at least one supporting rib.11. The window joint according to claim 10, wherein the rib extendscircumferentially on the window portion.
 12. A window joint system,comprising: a window joint interconnected in a casing string positionedin a first wellbore, the window joint including a sidewall having awindow portion through which a window is formed to drill a secondwellbore, the window portion having a reduced thickness of the sidewallprior to forming the window through the window portion.
 13. The windowjoint system according to claim 12, wherein the window portion has areduced weight, so that the window portion is oriented upwardly relativeto the first wellbore.
 14. The window joint system according to claim12, wherein the window portion has an inner diameter centerline which isin line with an inner diameter centerline of end connections of thewindow joint.
 15. The window joint system according to claim 12, whereinthe window portion has an inner diameter centerline which is laterallyoffset relative to an inner diameter centerline of end connections ofthe window joint.
 16. The window joint system according to claim 12,wherein the window joint further has an orienting profile formedinternally therein.
 17. The window joint system according to claim 16,wherein the orienting profile is rotationally aligned with the windowportion of the sidewall.
 18. The window joint system according to claim12, wherein the window portion has an outer diameter laterally offsetrelative to an inner diameter of the window portion.
 19. The windowjoint system according to claim 12, wherein the window portion has arecess formed externally on the sidewall to reduce the thickness of thesidewall.
 20. The window joint system according to claim 12, wherein thewindow portion has a recess formed internally on the sidewall to reducethe thickness of the sidewall.
 21. The window joint system according toclaim 12, wherein the window portion has an external radius formedthereon which reduces the thickness of the sidewall.
 22. The windowjoint system according to claim 12, wherein the window portion hasmultiple radii formed externally thereon.
 23. The window joint systemaccording to claim 12, wherein the window portion has multiple recessesformed in the sidewall, the sidewall between the recesses forming atleast one supporting rib.
 24. The window joint system according to claim23, wherein the rib extends circumferentially on the window portion. 25.A method of drilling a branch wellbore extending laterally from anintersection with a parent wellbore, the method comprising the steps of:interconnecting a window joint in a casing string, the window jointincluding a sidewall having a window portion with a reduced thickness ofthe sidewall; positioning the casing string in the parent wellbore;aligning the window joint with the window portion facing toward thedesired branch wellbore; cutting through the window portion of thewindow joint, thereby forming a window through the sidewall; anddrilling the branch wellbore through the window.
 26. The methodaccording to claim 25, further comprising the step of reducing thesidewall thickness in the window portion by laterally offsetting aninner diameter of the window portion relative to an outer diameter ofthe window portion.
 27. The method according to claim 25, furthercomprising the step of reducing the sidewall thickness in the windowportion by laterally offsetting an inner diameter of the window portionrelative to inner diameters of end connections of the window joint. 28.The method according to claim 25, further comprising the step ofreducing the sidewall thickness in the window portion by forming atleast one recess on the window portion.
 29. The method according toclaim 28, wherein the forming step further comprises forming supportingribs in the sidewall between multiple ones of the recesses.
 30. Themethod according to claim 28, wherein the forming step further comprisesforming the recess externally on the window portion sidewall.
 31. Themethod according to claim 28, wherein the forming step further comprisesforming the recess internally on the window portion sidewall.
 32. Themethod according to claim 28, wherein the forming step further comprisesforming at least one of the recesses internally and at least one of therecesses externally on the window portion sidewall.
 33. The methodaccording to claim 25, further comprising the step of reducing thesidewall thickness in the window portion by forming a radius externallyon the window portion.
 34. The method according to claim 33, wherein theradius intersects an outer diameter of the window portion.
 35. Themethod according to claim 25, wherein the aligning step furthercomprises rotationally orienting the window portion at least partiallyupwardly in the parent wellbore as a result of reduced gravitationalforce exerted on the reduced thickness sidewall of the window portion.36. The method according to claim 25, wherein the window joint includesan orienting profile formed therein, and further comprising the step ofrotationally orienting the profile relative to the window portion. 37.The method according to claim 36, wherein the cutting step furthercomprises engaging a deflector with the orienting profile, therebyrotationally aligning a deflector surface of the deflector with thewindow portion.